Avalanche Forecast

Issued: Dec 23rd, 2016 5:04PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

shorton, Avalanche Canada

South Rockies.

Wind slabs sit above a weak mid-pack, creating the potential for small avalanches to step down to deeper layers.

Summary

Confidence

Moderate -

Weather Forecast

SATURDAY: Flurries with accumulations of 5-10 cm, light southeast winds, alpine temperatures around -12C.SUNDAY: Dry and clearing, light northwest winds, alpine temperatures around -15C.MONDAY: Dry and clear, west winds increasing throughout the day reaching 50 km/h, alpine temperatures around -12C.

Avalanche Summary

On Thursday, two size 2 persistent slab avalanches were triggered with explosives in the southeast part of the region. The avalanches ran on weak faceted (sugary) grains between 50-100 cm deep. Earlier in the week, wind slabs were reactive to both explosive and human triggers (mostly size 2), while some stepped down produce larger persistent slab avalanches in the size 2.5-3 range. On Saturday, wind slabs are expected to be the primary concern resulting from new snow and strong to extreme southwest winds from earlier this week. There is a bit of uncertainty regarding how last week's snow will bond to old surfaces that formed during the cold snap. Due to these potentially persistent weak layers, wind slabs may remain sensitive to human triggering for some time. In the southeast corner of the region, there are concerns about a deep persistent problem. A weakness at the bottom of the snowpack has produced some large avalanches recently. Human triggering may be possible in thin areas or smaller avalanches have the potential to step down to this layer resulting in full depth avalanches.

Snowpack Summary

10-20 cm of new low density snow sits above 15-40 cm of settled storm snow. The storm snow has been redistributed into wind slabs in exposed terrain by strong to extreme winds. The new snow buries a variable surface that developed during the cold, dry, and windy conditions from earlier this month. This interface consists of scoured surfaces and wind slabs in wind exposed terrain, weak faceted (sugary) snow, and feathery surface hoar up to 20 mm in sheltered areas. In sheltered areas, there may be another layer of surface hoar in the upper snowpack which was buried around December 10. Observations have been limited, however, the reports we've received suggest the mid and lower snowpack are somewhat unconsolidated and faceting exists to varying degrees. Below treeline, the snowpack is very shallow and early season hazards such as stumps, rocks, and open creeks are still a major concern.

Problems

Wind Slabs

New snow adds to reactive wind slabs that sit over a variety of weak sliding layers. Use extra caution in steeper, wind-exposed terrain.

Use caution in lee areas. Recent wind loading has created wind slabs.Avoid slopes where the snow feels stiff or slabby.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

In thin snowpack areas, a layer of weak snow in the lower snowpack has been reactive recently in the southeast of the region. Triggering may be possible from thin snowpack areas, or smaller avalanches could step down to this layer.

Carefully evaluate and use caution around thin snowpack areas.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 24th, 2016 2:00PM